Field of the Invention
The present invention relates to a numerical controller capable of reducing machine load.
Description of the Related Art
Normally, in adjusting the acceleration and deceleration of a feed shaft and a spindle of a machine, the time required for the acceleration and deceleration is set as short as possible. By doing this, the cycle time of an entire machining program can be minimized. The higher the acceleration, however, the greater the mechanical shock is, resulting in a reduction in the life of the machine. A technique disclosed in Japanese Patent Application Laid-Open No. 2010-250697 is known as a conventional technique for automatically adjusting acceleration and deceleration.
As shown in FIG. 9, on the other hand, cycle times (hereinafter referred to as “tact times”) required for individual processes are settled in an automobile manufacturing line or the like. Since machining should only be finished within these tact times, shorter cycle times are not always preferable. In some cases, therefore, the time required for acceleration and deceleration should rather be increased, as long as it does not exceed the tact time, to minimize loads on the feed shaft and the spindle, thereby reducing the gradient of acceleration and deceleration.
Conventionally, manual adjustment is needed to set a large acceleration/deceleration time constant in order to reduce the gradient of acceleration and deceleration, and it is difficult to achieve the adjustment on the spot. According to the technique disclosed in Japanese Patent Application Laid-Open No. 2010-250697, the acceleration and deceleration can be automatically adjusted. However, this technique is designed to adjust the acceleration/deceleration time constant to achieve energy conservation, based on the correlation between the cycle time and the sum total of motor load currents and power consumptions of peripheral equipment, not considering suppression of vibration and shock on a machine.
Further, a conventional technique can be used to suppress vibration and chattering of a machine by automatically and dynamically changing the feed speed in accordance with a PMC ladder program or the like, based on input information on an impact sensor or motor load currents. According to this technique, however, no consideration is given to cycle times finally required by such a dynamic change of the feed speed.